1. Field of the Invention
Our present invention is directed to the preparation of high performance calcium borate modified overbased calcium sulfonate complex greases which are characterized by a combination of marked improvements in various properties over properties which have characterized certain types of heretofore known greases. The greases of the present invention are of the thixotropic type which comprise, advantageously, based upon the use of a mineral oil or equivalent oil medium in their production, as essential ingredients, oil-soluble calcium sulfonates derived from oil-soluble higher molecular weight sulfonic acids, which greases also contain calcium carbonate as calcite in extremely finely divided form, and also contain, as essential ingredients, calcium borate, and certain soaps, but they differ significantly and importantly from known prior art greases not only in their overall composition but, also, as indicated above, in various of the properties of such heretofore known greases.
2. Brief Description of the Prior Art
Thixotropic greases or greaselike overbased calcium sulfonate compositions having corrosion-inhibiting properties, and having utility for a variety of uses such as, for instance, in automobile and truck body undercoatings, and for various other purposes, are known to the art and are disclosed in various publications and patents, illustrative of which are U.S. Pat. Nos. 3,242,079; 3,372,115; 3,376,222; 3,377,283; 3,523,898; 3,661,622; 3,671,012; 3,746,643; 3,730,895; 3,816,310; and 3,492,231. Such greases or grease-like compositions have gone into quite widespread use either as such, or admixed with other ingredients to produce compositions for use in a variety of environments, and, generally speaking, they are characterized by reasonably good E. P. and antiwear properties, high dropping points, reasonably good resistance to mechanical breakdown, salt spray and water-corrosion resistance, thermal stability at high temperatures, and other desirable properties, as described in the aforesaid patents. Such heretofore known greases or grease-like compositions can be prepared by what is known as a 2-step process, as more particularly shown in the aforesaid U.S. Pat. Nos. 3,242,079, 3,372,115 and 3,492,231; or by what is known as a 1-step process, as is shown, for instance, in the aforementioned U.S. Pat. Nos. 3,671,012 and 3,746,643 which also disclose heretofore known 2-step processes.
U.S. Pat. No. 3,730,895 discloses grease thickeners and greases generally of the foregoing types wherein emphasis is placed on the necessity of utilizing, in the preparation thereof, a cloudy type of overbased calcium sulfonate in an oil carrier, the use of alkali or alkaline earth metal soaps of hydroxy fatty acids having about 12 to about 24 carbon atoms, and, in addition, also as a critical or essential ingredient thereof, a water-soluble corrosion inhibitor, illustrative examples of which latter are alkali metal and ammonium nitrites, carbonates, bicarbonates, sulfites, borates, chlorates, and perchlorates, as well as numerous other water-soluble corrosion inhibitors.
U.S. Pat. No. 3,492,231 discloses large numbers of overbased materials in the form of metal-containing single phase Newtonian solutions, for example, overbased calcium sulfonates, which it utilizes as intermediate materials for converting such solutions, by the addition thereto of so-called converting agents, to effect conversion of such solutions into the non-Newtonian thixotropic colloidal disperse systems to which the invention and the claims of said patent are directed. Among the metal-containing single phase Newtonian solutions disclosed in said patent, as generally noted above, are overbased calcium salts of sulfonic acids containing at least about 12 aliphatic carbon atoms exemplified by dodecylbenzene sulfonic acid, C.sub.12 -C.sub.40 mixed alkylbenzene sulfonic acids, dinonylbenzene sulfonic acid, and numerous other sulfonic acids as disclosed in said patent and in others of the above-disclosed patents and numerous other U.S. and foreign patents. These overbased single phase Newtonian solutions, according to U.S. Pat. No. 3,492,231, may have metal ratios as low as 1.1, although it also, and largely, discloses such solutions having materially higher metal ratios. While various processes are disclosed in said U.S. Pat. No. 3,492,231, and in numerous other patents and other printed publications, for preparing said overbased metal-or calcium-containing single phase Newtonian solutions, it is common practice to make them, as disclosed in said U.S. Pat. No. 3,492,231, by initially preparing a mixture or solution of a calcium sulfonate having a low metal ratio, e.g., 2 or 2.5, dissolved in a non-polar organic solvent, commonly a mineral oil; a metal base, for instance, calcium hydroxide; a so-called promoter, which permits the incorporation of excess metal, in this case, calcium, into the overbased Newtonian solutions; and carbon dioxide.
U.S. Pat. No. 3,492,231 discloses large numbers of diversified types of converting agents which, upon addition to the overbased Newtonian solutions of calcium sulfonates or other overbased metal-containing materials, usually coupled with heating and/or vigorous mixing, bring about the formation of the non-Newtonian colloidal disperse systems comprising the invention of said patent. These include, among many others, water; alcohols, for instance, methanol, isobutanol, n-pentanol and many others or mixtures thereof or mixtures of alcohols with water; alkylene glycols; mono-lower alkyl ethers of alkylene glycols such as monomethylether of ethylene glycol (methyl Cellosolve); and numerous others such as lower aliphatic carboxylic acids exemplified by acetic acid and propionic acid; ketones; aldehydes; amines; phosphorus acids; alkyl and aromatic amines; certain imidazolines; alkanolamines; boron acids, including boric acid; tetraboric acid; metaboric acid; and esters of such boron acids; and, also, carbon dioxide as such, or better in combination with water. The resulting non-Newtonian colloidal disperse systems of said patent may be in the form of gels or greases depending upon the particular conditions, proportions and ingredients which are utilized in the preparation thereof.
U.S. Pat. No. 3,492,231 also points out that, in those overbased Newtonian solutions in which the overbased materials are calcium sulfonates, the calcium carbonate which is formed during the preparation of said Newtonian solutions appears to be in amorphous form whereas, when said Newtonian solutions are converted into the non-Newtonian colloidal disperse systems, the dissolved amorphous calcium carbonate salt or complex is transformed into solid crystalline metal-containing particles of calcium carbonate, usually in the form of calcite, which then grow to form particle sizes which may range in size from about 40 to 50 Angstroms (A.) or larger, for instance, up to 1000 A. or even up to about 5000 A..sup.1 FNT 1. Under certain conditions, and in certain cases only, in the conversion step, the solid calcium carbonate which forms is not solely calcite but contains some vaterite. This does not appear to adversely affect the production of the greases of our invention.
It has also long been known to the art, as shown in U.S. Pat. No. 2,607,735, to prepare substantially anhydrous calcium soap greases which consist essentially of a lubricating oil containing, as a thickener, from 5 to 30% by weight of a calcium soap of a mono-and/or di-hydroxy substantially saturated fatty acid containing from 12 to 24 carbon atoms and exemplified by the calcium salt of 12-hydroxystearic acid. This patent points out that the calcium salts of the aforesaid hydroxy fatty acids have improved properties over the calcium salts of non-hydroxy C.sub.12 to C.sub.24 fatty acids in that the calcium salts of the hydroxy C.sub.12 to C.sub.24 fatty acids have much greater high temperature properties than the calcium soaps of the corresponding non-hydroxy C.sub.12 to C.sub.24 fatty acids, and, further, that very substantial improvement results from the inclusion in the calcium soap greases of the invention of said patent of from about 1 to 10 wt. % of low molecular weight salts such as calcium acetate and calcium propionate. This patent states, further, that salts of certain inorganic compounds, for example, those of boric acid and its derivatives, may also be incorporated into the calcium soap greases of the invention. It notes that a conventional lime soap grease becomes unstable at temperatures around the boiling point of water, for example above 200.degree. F.; whereas, when the C.sub.12 to C.sub.24 hydroxy fatty acid calcium salts or soaps are substituted for the corresponding calcium salts or soaps of the C.sub.12 to C.sub.24 non-hydroxy fatty acids, the melting point and the useful range of lime soap greases may be raised about 70.degree. F. to 100.degree. F. or more. The addition, further, to said greases made from the aforesaid calcium salts or soaps of the hydroxy fatty acids, of the lower molecular weight salts such as calcium acetate and calcium propionate, is stated to raise the high temperature range by as much as an additional 200.degree. F. or so. The patent points out, additionally, that the inclusion in the calcium soap greases of the calcium acetate raises the dropping point of the greases very materially, whereas others, such as boric acid, do not so materially raise the melting point but appear, nevertheless, to be valuable ingredients in further stabilizing the greases at higher operating temperatures. In Example V of the patent, a grease made in accordance with the patent is disclosed in which calcium borate is used (formed upon neutralization of the boric acid with calcium hydroxide) which is stated to be of particular interest because of the low cost of boric acid and because, under conditions where extremely high temperature is not encountered, the calcium soap borate greases of the patent have very satisfactory properties. This Example V grease exhibited about a 10% oil loss, characterized as a somewhat high loss, at 225.degree. F., and it lost viscosity rapidly at higher temperatures. The patent states that, nevertheless, the grease of Example V appears to be quite satisfactory for lubrication at temperatures up to about 250.degree. F., and that spindle tests at 250.degree. F. and at 10,000 R.P.M. showed a useful life of 1000 hours which is asserted to be remarkable for a lime base grease.
That the greases of U.S. Pat. No. 2,607,735 are radically distinguished from those of our present invention is apparent, apart from other aspects or considerations, from the following facts. Whereas said patent, in Column 5, Lines 18-24, emphasizes "that a grease stable at temperatures above 225.degree. F. apparently can not be prepared from ordinary calcium stearate and the corresponding borate" whereas, on the other hand, "The soaps of hydroxy acids * * * seem to combine very well with the salts of boric acid to form a grease stable at reasonably high temperatures, i.e. temperatures ranging around 225.degree. to 250.degree. F." In sharp contrast thereto, the greases of our present invention can use, as the soap content thereof, conventional soap-forming acids, e.g. stearic acid or oleic acid, and there are obtained greases which have excellent high temperature stability as measured by the dropping point as demonstrated by the following data:
______________________________________ Soap-Forming Acid Grease Penetration Dropping Point ______________________________________ Stearic Acid 315 500.degree. F. Oleic Acid 332 500.degree. F. 12-Hydroxy- 295 500.degree. F. stearic Acid ______________________________________
Furthermore, infra-red scans of greases made in accordance with our present invention differ radically from those greases made in accordance with the invention of U.S. Pat. No. 2,607,735, indicating that the greases of our invention and the greases of the invention of said patent clearly differ from each other compositionally, structurally and in various of their properties and utilities.
In short, the grease compositions of U.S. Pat. No. 2,607,735 are not of the type to which our present invention relates, namely, thixotropic overbased calcium sulfonate greases; they are inferior in numbers of respects to the greases of our invention and they do not possess many of the advantageous properties which characterize the greases of our invention.
None of the foregoing patents, or any other patents or printed publications dealing with the preparation of greases or grease compositions, of which there are very large numbers, discloses or suggests, so far as we are aware, the novel grease compositions of our present invention or the preparation thereof, nor, of course, the improved results which are obtained by the grease compositions of our invention, which we disclose and describe below.
Prior art greases or grease compositions, such as, for instance, those disclosed in U.S. Pat. Nos. 3,242,079; 3,372,115; and 3,376,222, which embody therein calcium or other alkaline earth metal sulfonates and extremely finely divided solid particles of calcium carbonate, generally in the form of calcite, with due regard for various of their favorable properties, also, generally speaking, suffer certain significant and material disadvantages. For instance, they possess inherently poor pumpability, being essentially unpumpable at low temperatures or room temperatures, as well as somewhat above room temperature, due to their extremely tacky consistency, thereby reducing relatively low temperature applicability. This, in itself, is a very substantial deficiency because it complicates the ability to handle such greases and limits their utility for a number of uses which they might otherwise be able to fulfill. Still another of their disadvantages, viewed from an economic standpoint, is due to the large amount of calcium sulfonates required to provide a fully satisfactory grease consistency since such greases are, generally speaking, expensive to produce, which limits their commercial value because greases are, in the main, low cost items and anything which results in appreciably increasing the cost of greases presents an important disadvantage in limiting the extent and field of use thereof. These, and other, disadvantages of such known greases and grease compositions are overcome by the novel greases and grease compositions of our present invention, since, in the first place, the pumping characteristics of the greases of our invention are comparable to those of known types of greases where there is no such problem. Additionally, greases and grease compositions made in accordance with our invention, at least in many or most cases, perform at least equally well and, in many cases, decidedly better compared with heretofore known commercial high performance multipurpose greases, a situation which is not the case with the strictly calcium sulfonate greases of the type disclosed in the illustrative aforementioned patents. The greases of our invention are characterized by high dropping points and by other advantageous multipurpose properties, thereby adapting them for a wide variety of uses in different environments.